Plastic

Plastic is a vast category of synthetic or semisynthetic materials. These materials are primarily composed of polymers, which are long molecular chains. The defining feature of plastic is plasticity. This term refers to the ability of a material to be molded, extruded, or pressed into many different solid forms. This adaptability makes plastic incredibly useful for modern life. It is often lightweight, durable, and resistant to chemicals. Because it is inexpensive to produce, it is used in almost every industry worldwide.

To understand how plastic works, we must look at its molecular structure. Most plastics consist of organic polymers. These polymers are built from long chains of carbon atoms. These chains are made of many repeating units called monomers. The main path of the chain is called the backbone. To change how a plastic behaves, scientists add side chains. These side chains hang from the backbone and are attached to the monomers. The specific structure of these side chains determines the final properties of the material.

Scientists classify plastics in several different ways. One common method is by their chemical structure. This includes groups like acrylics, polyesters, silicones, and polyurethanes. Another method is by the chemical process used to make them, such as condensation or cross-linking. Plastics can also be grouped by physical properties. These properties include hardness, density, and thermal resistance. Some plastics are even classified by how they react to radiation or organic solvents.

A vital classification is based on how plastics react to heat. Thermoplastics are materials that do not undergo a chemical change when heated. They can be melted and molded into new shapes many times. Examples include polyethylene and polyvinyl chloride (PVC). In contrast, thermosetting polymers, or thermosets, can only take a shape once. After they solidify, they stay in that shape permanently. If you apply high heat to a thermoset, it will decompose rather than melt.

Thermosets often consist of closely cross-linked polymers that hold the structure together.

The history of plastic began in the early 20th century. The first fully synthetic plastic was Bakelite. Leo Baekeland invented Bakelite in New York in 1907. Baekeland is also the man who coined the term "plastics." Since then, many scientists have advanced the field. Hermann Staudinger is often called the father of polymer chemistry. Herman Mark is known as the father of polymer physics. Their work helped turn materials science into a sophisticated discipline.

Today, the scale of plastic production is enormous. Between 1950 and 2017, an estimated 9.2 billion metric tons of plastic were produced. More than half of that total was made since 2004. In 2023, preliminary figures showed over 400 million metric tons were produced. About 80% of this is known as commodity plastic. These are inexpensive plastics used for mass-produced items like packaging and food containers. In 2015, packaging alone consumed 146 million metric tons of commodity plastic.

Engineering plastics make up about 20% of global production. These are more expensive and much stronger than commodity plastics. They are often used in specialized applications like vehicle parts. In modern cars, plastic can replace metal to reduce weight. This can improve fuel efficiency by 6% to 8%. Even though cars are about 50% plastic by volume, plastic only accounts for 12% to 17% of the total vehicle weight.

Despite its benefits, plastic creates major environmental challenges. Most plastic produced has not been reused. Only about 9% of all plastics are recycled globally. About 14% of discarded plastic has been incinerated. This means much of it ends up in landfills or as pollution. An estimated 8 to 12 million tons of plastic enter the oceans every year. This pollution often creates garbage patches in the sea. There is also great concern regarding microplastics, which are tiny particles that can threaten ecosystems and human health.